Glucocorticoid modulation of prolactin receptors on mammary cells of lactating mice

Prolactin receptors were monitored by measuring ¹²⁵I-labeled prolactin binding to collagenase-dissociated mammary epithelial cells of lactating BALB/c mice. Specific receptors for iodine-labeled prolactin with an apparent dissociation constant (K_d) of 0.99 · 10^?9 M were present on the dissociated mammary cells. The binding was inhibited by ovine prolactin, human growth hormone and human placental lactogen but not by follicle stimulating hormone, luteinizing hormone, thyroid stimulating hormone, bovine growth hormone or insulin. Adrenal ablation of nursing mothers caused a reduction of the number of prolactin receptors and this effect was preventable by hydrocortisone therapy. Hydocortisone injections to mothers 3 days after adrenalectomy also induced a replenishment of the prolactin receptors on the mammary cells. Injections of progesterone failed to sustain the high level of mammary cell prolactin receptors in adrenalectomized animals. Stimultaneous injections of hydrocortisone and progesterone to animals 3 days after adrenalectomy caused a partial suppression of the stimulatory action of hydrocortisone alone. The results suggest that hydrocortisone can exert a modulatory influence on mammary cell prolactin receptors in non-hypophysectomized post-partum mice without altering the dissociation constant (K_d) of the receptors.     

Tubulin increases with lactation in rat and guinea pig mammary alveolar cells

Summary Changes in mammary gland tubulin were studied immunocytochemically during transition from late pregnancy to lactation. Indirect immunofluorescence was used to localize tubulin in mammary glands from late pregnant, early lactating and peak lactating guinea pigs. Whole rabbit antiserum against guinea pig brain tubulin and affinity-purified antibody indicated increases in alveolar cell tubulin content from late pregnancy through peak lactation coincident with the development of lactation. Only alveolar cells displayed high, specific fluorescence or underwent a developmental increase. Tubulin was concentrated apically, in association with secretory structures. In a second study comparing mammary tissues from 18 days pregnant and 10 days lactating rats, EM immunogold was used with three commercial antitubulins ranging from a rabbit polyclonal antiserum against chick brain MTs to a monoclonal mouse anti-alpha tubulin. Gold particle counts indicated 2- to 5- fold tubulin increases in alveolar cells with lactation and development of an apicobasal (high apical) tubulin gradient. Variations among the three anti-tubulins is discussed. The results confirmed previous observations of whole gland tubulin increases based on colchicine binding assays and localized the site of the increase primarily in alveolar cells.Abbreviations EM electron microscope-(ic) - GAM goat anti-mouse - GAR goat anti-rabbit - Ig immunoglobulin - MC monoclonal - MT microtubule - PAGE polyacrylamide gel electrophoresis - PIPES 1,4-piperazine diethane sulfonic acid - PBS phosphate buffered saline - PC polyclonal - Rb rabbit - SDS sodium dodecyl sulfate Dedicated to Professor Stuart Patton on the occasion of his 70th birthday.